There can be several ways to upload files, pictures, pdfs and so on, and use them in your articles.

Media Manager

In the admin area go to Site->Media Manager.

Navigate to the folder you want to upload in, for example stories->food.

At the page bottom is a section to browse for a file and "Start Upload".
Your file will now be available for inclusion in articles.
Place the cursor in the article where you want the image to appear and click on the 'Insert/Edit Images' icon
You will have to know the path to the image, for example "images/stories/myimage.gif"

While Editing

Joomla provides a link to the media manager at the bottom of the editing window.

JCE Editor

The JCE editor can also upload files using its enhanced 'image manager'.
Place the cursor in the article where you want the image to appear and click on the 'image manager' icon
The Image Manager Window.

On the right side, above the 'Details' section are icons to create folders, upload files and get help with the Image Manager.

eXtplorer

Another extension that can upload files is eXtplorer. Clicking on it's up arrow icon brings up a dialog box where you can upload multiple files.